The present invention relates to removable thin film mountings for photomasks used in the manufacture of semiconductor devices. It is well known that pattern transfer from the photomask to substrate is accomplished by exposing the mask to a light source. The patterns on the photomask are projected onto the substrate which has been treated with a photo-sensitive substance. Any foreign substance on the surface of the mask will interfere with the proper pattern being transferred to the substrate.
To eliminate particulate surface contamination of the mask surface, a framed thin film known as a pellicle is mounted on the mask surface, so that any contamination which would ordinarily be deposited on the mask surface, is held off from the surface by the pellicle. The frame supports the film at a sufficient distance from the mask surface that any particles on the film will be out of focus during the lithographic process, and therefore will not be projected onto the substrate.
Currently, pellicles are mounted directly to the surface of the mask by use of a double-sided adhesive. When it becomes necessary to replace the pellicle, the entire pellicle is removed from the mask. The adhesive often leaves residue on the mask surface, requiring the use of cleaning agents. However, this very act of cleaning the mask can increase contamination. Therefore, following the cleaning procedure, reinspection of the mask is required to ensure that its original quality has not been affected by the cleaning process. All of this increases the cost of pellicle replacement in terms of time, money and potential damage to the mask.
The present invention overcomes the drawbacks of the prior art by providing a composite frame for a free-standing membrane which includes a first member, means for mounting the first frame member to a planar surface such that a working area is defined on the planar surface, a second frame member having a first side for peripherally supporting the membrane, and means for removably mounting a second side of the second frame member to the first frame member so that the membrane protects and covers the working area.
Another aspect of the invention is a method for using a pellicle, which includes the steps of mounting a first frame member to a planar surface such that a working area is defined on the planar surface within the frame, and removably mounting a framed thin film or pellicle to the first frame member so that the working area is protected by the pellicle. In the event the pellicle needs to be replaced, the old pellicle is merely disengaged from the first frame member, and a new pellicle is mounted in its place. The first frame member remains in place on the planar surface so that the pellicle does not have to be directly affixed by adhesive to the planar surface.